1. Field of the Invention
The present invention is related to Voice over Internet Protocol (VoIP), communications and more particularly, to VoIP communications networks with softswitch support.
2. Background Description
Broadband Internet connections have become ubiquitous. A typical Small Office, Home Office (SOHO), for example, may have a private network where a router couples local devices on the home/office network to a broadband modem, e.g., cable or Digital Subscriber Line (DSL) modem. Typically also, a Dynamic Host Configuration Protocol (DHCP) server residing in the router manages the private network, assigning each connected device a local, private IP address. The broadband modem has a public Internet Protocol (IP) address and connects over high-speed digital cable or a DSL line to the Internet.
Typically, router uses the public IP address on the modem side and exposes a private IP address (usually the DHCP server assigns 192.168.0.1 to the router) on the private network. Typically also, the DHCP server assigns a private IP address (having the form 192.168.0.xxx) to each private network device, i.e., on the home/office side. Frequently, the router also provides Network Address Translation (NAT). If a private network device accesses the Internet, the router opens a port on the modem side. Then using NAT, the router changes the source private IP address and port in the IP header to match the modem's public IP address and newly opened port. Incoming messages for the private network device are then received on the opened port. The router reverses modification of the IP header by changing the destination IP address and port back to the private IP address and port of the private network device. This works fine as long as the body of a message (known as the “payload”) itself does not contain IP addresses.
Commercial telecommunications platforms have evolved digital telecommunications devices that allow service providers to deliver IP based telecommunications services. Digital communications such as Voice over IP (VoIP) may, for example, use Session Initiation Protocol (SIP) and Media Gateway Control Protocol (MGCP) for establishing and clearing connections between network stations. See, RFC3722 for SIP messaging standards and definitions. SIP based VoIP calls work well for a relatively simple connection with simple user control, e.g., a single user connected directly to the Internet using a typical user interface. These state of the art connection-oriented signaling protocols extensively embed IP addresses in messages.
Unfortunately, embedding IP addresses in VoIP communications messages can produce serious problems communicating with devices behind a router with activated NAT. Normally, state of the art connection-oriented signaling protocols attempt to route messages to the contact uniform resource indicator (URI) of a registered device. However, as noted hereinabove, in a private network this contact URI is a private IP address. So, instead of being directed to the public IP address of the broadband modem and the respective opened port on the router, return VoIP messages are directed to the not publicly routable private IP address. This private IP address may also be the same for any number of devices on other private networks.
A softswitch is a device that allows multiple contacts for the same user or multiple users to connect from the same device. Including a softswitch for a private communications network may exacerbate the above problem. Consequently, without more, a SIP registrar/SIP server cannot direct messages to SIP devices on a typical private network connected behind a broadband router and, therefore, the SIP server may not be able to reach SIP devices.
Session Border Controllers (SBC) have been added to typical private networks to address this problem. A typical state of the art SBC is a Back-to-Back User-Agent (B2BUA), inserted on the border between 2 distinct networks. The SBC solves NAT problems for network devices in either of the two networks. In VoIP networks SBCs are usually located in what is known as the demilitarized zone (DMZ) of a data center and is the single point of entry for VoIP communications. SBCs provide security for data centers and solve the problems introduced in SIP or MGCP signaling because of NAT devices in the network. For each VoIP device that registers with the SBC, the SBC creates a unique port between the SBC and softswitch and listens on each port.
Opening multiple ports increases the number of active IP connections that the SBC and the softswitch must maintain. Maintaining these connections consumes processing power in the connected devices. Moreover, increasing connections increases network complexity. Also, SBCs may change the user part of the respective contact URI, which causes problems in SIP Registrars that rely on the user part to detect that a user is registering from multiple locations. Parsing and maintaining attached URI tags increases processing power consumption because internally, address associations are based on IP:port structures.
Thus, there is a need for minimizing power consumed in VoIP communications and, more particularly for simplifying SIP communications while minimizing the number of connections between SBCs and softswitches in a typical private network.